text: Natural products may be extracted from the cells, tissues, and secretions of microorganisms, plants and animals. A crude (unfractionated) extract from any one of these sources will contain a range of structurally diverse and often novel chemical compounds.  Chemical diversity in nature is based on biological diversity, so researchers collect samples from around the world to analyze and evaluate in drug discovery screens or bioassays.  This effort to search for biologically active natural products is known as bioprospecting.
  Pharmacognosy provides the tools to detect, isolate and identify bioactive natural products that could be developed for medicinal use.  When an "active principle" is isolated from a traditional medicine or other biological material, this is known as a "hit".  Subsequent scientific and legal work is then performed to validate the hit (e.g. elucidation of mechanism of action, confirmation that there is no intellectual property conflict).  This is followed by the hit to lead stage of drug discovery, where derivatives of the active compound are produced in an attempt to improve its potency and safety. In this and related ways, modern medicines can be developed directly from natural sources.
  Although traditional medicines and other biological material are considered an excellent source of novel compounds, the extraction and isolation of these compounds can be a slow, expensive and inefficient process.  For large scale manufacture therefore, attempts may be made to produce the new compound by total synthesis or semisynthesis. Because natural products are generally secondary metabolites with complex chemical structures, their total/semisynthesis is not always commercially viable.  In these cases, efforts can be made to design simpler analogues with comparable potency and safety that are amenable to total/semisynthesis.